4
The necessity of such a ridiculous idea as "proof of age" is made more obvious by the fact that the "clothing" in the video in question is relatively tame. Wouldn't want to be subject to complaints that you're sexually objectifying minors, oh no!

Try this one (no nudity; but may not be appropriate for some workplaces).

5
Some people just mark all their stuff R-18 because they don't want to deal with complaints that item X is too skimpy.

Brick's comment is... in the early days of the industry there was a lot of adult content, but clearly they were massively uncomfortable with porn with identifiable schoolgirls. So a lot of things got "translated" into "colleges" where all the girls happened to wear sailor suits etc. "She's not under 18, honest!" That's mostly fallen by the wayside as the bluenoses pretty much ignore anime (Japan is massively inconvenient to their narratives and thus they usually pretend it doesn't exist.)

The back half of the comment is something that you saw on a lot of domestic porn from fairly recent, where you'd see that kind of disclaimer before the show.

7
It used to be that every J track at Amazon was tagged "[Explicit]" - even instrumental ones. Unfortunately, that was actual text in the track title, encoded on MP3, and not even in Comment like "Amazon Song ID: XXXXXX". Fortunately Amazon has moved on from that particular idiocy.